1. Field of the Invention
The present invention relates to a thin film transistor and a fabrication method thereof, and in particular to an improved method for fabricating a thin film transistor including forming a gate electrode and impurity regions by a self aligning process and a thin film transistor resulting therefrom.
2. Description of the Background Art
A conventional thin film transistor fabrication method is shown in FIGS. 1A-1D of the accompanying drawings.
In FIG. 1A, a gate electrode 2 is formed on an insulation substrate 1. The gate electrode 2 results from forming an impurity-doped polysilicon film on the substrate 1 by applying a chemical vapor deposition method and a photoetching method using a gate mask.
As shown in FIG. 1B, a gate insulation film 3 is formed by depositing an insulation member on a front surface of the insulation substrate 1 including the gate electrode 2, and an active layer 4 is formed on the gate insulation film 3 using the chemical vapor deposition method.
As shown in FIGS. 1C and 1D, a photoresist member is coated on the active layer 4, and the resultant structure is subsequently patterned using the photo-etching method, thus forming a photoresist film pattern 5. Then, a p-type impurity (B, BF.sub.3, etc.) or an n-type impurity (As, P, etc.) is implanted into the exposed portion of the semiconductor film (active layer 4) using the photoresist film pattern 5 as a mask, thus defining impurity regions 6a and 6b, so that the thin film transistor is fabricated. The photoresist film pattern 5 defines a channel region "b" of the active layer 4 corresponding to the gate electrode 2 and an offset region "c" between the impurity regions 6a and 6b. The impurity regions denote a source "a" and a drain "d", respectively.
In the above-described conventional thin film and a fabrication method thereof, the off current is largely varied depending on the degree of the alignment which defines the lengths of the channel region and offset region, so that the reliability and productivity of the device are decreased.